Moisture responsive control apparatus



g 1954 G. w. GUSTAFSON 3,143,610

MOISTURE RESPONSIVE CONTROL APPARATUS Filed Oct. 1, 1958 6 3 64 7; ,?4 63 62 23 I3 2 A ,65 2 z LEI K l2 i J 75 74 I 52 15''" 5 73 ,r- MOISTURE RESPONSIVE v 0 I ELEMENT j 42 fff l 44 7 3 Fig. 5

INVENTOR. GORDON W. GUSTAFSON United States Patent() 3,143,610 MOISTURE RESPQNSIVE CGNTROL APPARATUS Gordon W. Gustafson, Mound, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Filed Get. 1, 1958, Ser. No. 764,620 18 Claims. (Cl. ZOO-61.06)

The present invention is concerned with a moisture responsive control device; in particular, a device containing a thin ribbon type moisture responsive element which is made up of two parallel portions formed by looping the element over one support and connecting the extremities of the element to another support.

With the increase in residential air conditioning, and residential humidification and de-humidification equipment, the demand for a relatively accurate and yet inexpensive moisture responsive control device has greatly increased. In the present invention, a small compact control device is provided having a reasonable accuracy and yet a low cost.

Therefore, an object of the present invention is to provide an improved moisture responsive control device.

Another object of the present invention is to provide an improved moisture responsive control device with a thin ribbon type sensing element made up of two portions by looping a continuous element over a movable support and connecting the joined ends of the element to another support.

And still another object of the present invention is to provide an improved moisture responsive control device in which the moisture responsive element can be relaxed or placed under tension through the control point setting adjusting means to provide a positive on or a positive 011 of the associated controlled apparatus.

And still another object of the present invention is to provide an improved moisture responsive control device having a thin ribbon moisture responsive sensing element which is strung over a roller for equalizing the tension in the two sections of the element as well as the tension across the element between its opposite edges.

These and other objects of the present invention will become apparent upon the study of the following specification and claims of which:

FIGURE 1 is a front view of the control device with a portion of the cover cut away to show the operating mechanism.

FIGURE 2 is a vertical section view of the device of FIGURE 1.

FIGURE 3 is a partial side view of the device shown in FIGURE 1.

FIGURE 4 is a cross-sectional view of a roller supporting the sensing element of the device shown in FIG- URE 1.

FIGURE 5 is a sectional view of the operating'mechanism associated with the switch of the device shown in FIGURE 1.

FIGURE 6 is a partial cross-sectional view similar to that of FIGURE 2 showing the mechanism in a positive off position.

Referring to FIGURE 1, the control device has a base or frame 10 which has a cover 11. A bracket 12 which is attached to an upper end 13 of the base extends downward into a chamber 14 formed by base 10 and cover 11. A lever or arm 15 is pivotally attached to the upper end of bracket 12 near end 13. Another lever or arm is pivotally connected to the free end of lever 15 and extends in the same direction, so that levers 15 and 20 make up a support lever for one end of a moisture responsive element 21. The relationship of lever 20 with respect to lever 15 and thus the position of the upper end of element 21 is determined by the position of screw22.

3,143,61h Patented Aug. 4, 1964 The factory calibration of the instrument is accomplished by rotating screw 22. Lever 20 is made of bimetal and provides temperature compensation to the device.

A screw 23 is threaded into upper end 13 to extend into chamber 14. A coil spring 24 compressed between the lower end of bracket 12 and arm 15 biases arm 15 in an upward direction against the end of screw 23. By the rotation of a knob 25 attached to screw 23, the control point of thedevice is adjusted.

In the lower portion of chamber 14, a snap switch 31 is attached to the base. The snap switch is a conventional type having an operating plunger or button 31. Upon moving plunger 31 inward, the switch is operated after the external force is great enough to load a resilient contact member to snap the mechanism and open the circuit connected to terminals 32 and 33. Obviously the type of switch and whether it opens or closes upon the operating button being moved inward are no part of the present invention, but such change would be obvious to one skilled in the art.

A bracket 40 attached to base 10 pivotally supports a lever 41 about an axis 42. Lever 41 engages operating button 31 when it is moved in a counterclockwise direction. A spring 43 is connected between lever 41 and base 10 to apply a counterclockwise force to lever 41. Spring 43 accomplishes the preloading of switch 30, so that the element 21 need only furnish a small force for operating the switch. Attached to one extremity 44 of lever 41is a roller 45. The roller is mounted on a pin or shaft 50 which is held in position by looping one end 51 of the pin into a notch of lever 41.

The sensing element 21 is a thin ribbon of moisture responsive material which expands upon an increase in the moisture content of the air surrounding the element. The specific material used is a condensation product of 1,6-hexanediamine and adipic acid more commonly known as nylon. The element has appreciable stiffness to afford some resistance to bending. The ribbon element is formed of two parts by looping theelement over a bar or roller 45 and connecting the ends of the elementby a clamp 52 to the free end of arm 20. The roller 45 equalizes the tension on the two adjacent portions of the element.

Referring to FIGURE 3, a clip or clamp 53 is attached to the roller to hold the element 21 against the curvature of the roller. This clip is necessary since the nylon ribbonis stiff and does not conform to the curva- -made to conform to the surface of the roller; so that, as

the element contracts and pulls upward on the roller and lever 41, there is no significant change in the position of the element with respect to the roller.

Referring to FIGURE 4, roller 45 is shown mounted on shaft 50. The portion 60 of the roller which contacts the shaft as it passes through the center of the roller is small with respect to the width of the roller and is slight ly off center as measured from the ends of the roller. Since the shaft has a diameter slightly less than the hole through the roller, roller 45 is able to pivot about the shaft in a plane of the drawing as shown in FIGURE 4. With the wide ribbon element 21 wound around the roller, .the free movement of the roller with respect to the shaft 50 is important in equalizing the tension which might exist in the ribbon from one edge to the other.

The tension of the two sections of the element is equalized by the rotation of the roller, and the tension between lever' 41 counterclockwise.

the edges of the ribbon is equalized by rocking the roller about shaft 50 either clockwise or counterclockwise looking at the roller in FIGURE 4. A notch 61 is shown in the outer surface of the roller at one side. The notch is used for identification purposes since the element is the possible looseness in the threads of screw 23. Spring 63 has a projection 64 which engages a hump 65 on the disc to act as a limit stop for the control point setting when reaching the dry extremity of its adjustment. As knob 25 isrotated to rotate screw 23 clockwise as shown in FIGURE 2, hump 65 will engage projection 64. At the same time, a bump 70 on the lower side of disc 62 engages a raised portion 71 on arm 15. Arm is moved downward to lower the upper extremity of element 21 to allow lever 41 to pivot clockwise and operate the switch 30 to a closed position. of disc 62 is known as the positive on or dry position.

A rod or shaft 73 extends between the control point adjustment mechanism and switch 30. The upper portion 74 of rod or lever 73, as shown in FIGURE 2 is -pivoted about bracket 75 attached to the base and is bent in a horseshoe shape. The free end portion 80 of horseshoe-shaped portion 74 of lever 73 engages the periphery of disc 62. A notch 81 in disc 62 opposite projection 70 is adapted to receive end portion 80 when The extreme clockwise position disc 62 is rotated in a counterclockwise direction for lever 41 to move the lever against the operating button 31 of the switch.

Operatiom As shown in FIGURE -1, the moisture responsive control device is set to control at some predetermined level .of moisture in the air surrounding element 21. For explanation purposes, let us assume that switch 30 is closed and the circuit connected between terminals 32 and 33 is closed to operate dehumidification apparatus. Upon a decrease in the moisture content of the air surrounding element 21, the element 21 will contract to pivot The upper portion 84 of lever41 engages operating button 31 of the switch to open the switch. The moisture content of the air surrounding element 21 would then increase until the element elongated a sufficient amount to rotate arm 41 clockwise to close the switchand start the dehumidification apparatus.

For a given setting of the instrument as determined by the position of knob 25, any change in the ambient temperature is compensated for by the movement of the right extremity of arm 20 since the arm is made of temperature responsive bimetal.

For a better understanding of the advantage of clip I 53 on roller 45 for holding the nylon element 21 in conformity with the roller surface, the operation of such a 6 device without clip 53 will be considered. With an ele- .ment having an appreciable stiffness and thereby resisting Projection 65 again engages spring end 64 to roller to clamp 52, but the sections would bow outward depending upon the stiffness of the element. As the element contracted and a force was developed to overcome the normal operating resistance of the switch, some of this force would decrease the degree of non-conformity of the ribbon, so that the ribbon actually wrapped around the curved surface of roller 45 without looping out as far. This resilient action on the part of the ribbon in not conforming to the curvature of the roller 45 would interpose an error in the operation of the device.

With the use of clip 53, the resilient element 21 is made to conform to the curvature of roller 45, so that the adjacent portions of the element lay practically parallel between roller 45 and clip 52. Upon the increase in the tension of the element as it contracts by a lower humidity content in the surrounding air, the full movement ofithe contraction is applied through roller 45 to move lever 41.

In order to insure that the tension placed on element 24 is not beyond its elastic limit, spring 21 acts as the strain release spring. Once upper end 84 of arm 41 engages the operating button of the switch and the switch is actuated, no further movement of arm 41 can exist.

Should the element continue to decrease in length, a limit 7 on the tension of the element is determined by the com- As the position of arm 41 changes, the tension on the .two portions of element 21 can vary. Since the element is looped over roller 45, the tension on the two portions -of the element will equalize by a small movement of the roller.

At the same time, the strain on the element from one edge to the other is equalized by the position roller 45 takes with respect to the shaft in the plane of the paper as shown in FIGURE 4. Such an unequal tension in that direction might take place due to a screw in the ribbon itself during manufacture or due to the build up of tolerances in the device. By the novel means of supporting roller 45 on shaft 50, the axis of roller 45 is insured perpendicular to the length of the ribbon and'no unequal tensions exist across the ribbon from edge to edge.

To provide a positive off, the knob 25 is rotated to turn screw 23 in a counterclockwise direction as shown in FIGURE 2. The end of shaft 73 rubs along the periphery of disc 62 until it is received in the notch 81. Further movement of disc 62 in a counterclockwise direction pulls the horseshoe-shaped end '74 in a clockwise direction until it rests in a position as shown in FIGURE 6. In this position, the lower end 83 of shaft 73 is moved in a clockwise direction, as shown in FIGURE 6, to engage upper portion 84 of operating lever 41 to apply a force to operating button 31 of the switch. The positive off limit of the rotation of knob 25 is determined by the engagement of raised portion 65 and spring 63.

For a posltive on operation of the control, knob 25 'is rotated to turn screw 23, as shown in FIGURE 2, in

a clockwise direction. When the projection 70 on the -lower side of disc 62 engages projection 71 on the upper side of arm 15, arm 20 is moved downward to relax element 21. Lever 41 is then moved in a clockwise direction as shown in FIGURE 1 to operate switch 30.

While the invention has been described and disclosed as a moisture responsive element, the intention is to limit the scope of the invention only by the appended claims in which I claim:

1. In a moisture responsive .device, a frame, a first lever pivotally mounted on said frame, an adjustment screw received by said frame and engaging said lever, a second lever pivotally mounted on said frame, control means, said second lever being adapted to operate said control -means when pivoted in a first direction, a spring connected between said second lever and said frame for biasing said second lever in said first direction, a thin ribbon .moisture responsive element, a roller connected to said the device.

said control means.

2. In a moisture responsive device, a frame, a first lever pivotally mounted on said frame, an adjustment screw received by said frame and engaging said lever, a second lever pivotally mounted on said frame, control means,

said second lever being adapted to operate said control means when pivoted in a first direction, a spring connected between said second lever and said frame for biasing said second lever in said first direction to preload said control means, a thin ribbon moisture responsive element,

a roller connected to said second lever, means connecting the ends of said ribbon to said first lever and looping said ribbon over said roller so that upon contraction of said element upon a change in moisture said second lever is 'moved in said first direction, said roller equalizing the actuating said switch, a lever attached to said base and engaging said member, said lever having a free end, a first member pivotally attached to said: free end of said lever said first member being free to pivot about an axis and about a point between its ends in a plane of said axis, and a moisture responsive ribbon, said ribbon being wrapped over said first member and attached to said member whereby upon a change in the length of said ribbon as moisture level changes said lever pivots to actuate said switch, said first member providing for the equalization of. tension between separate portions of said ribbon and said first member can rock to maintain the tension between opposite sides of said nibbon equal.

4. In a moisture responsive device, a frame, anoperating lever attached to said frame, a thin ribbon type moisture responsive element, a round surface member attached to said lever, said element being looped over said member and having its extremities attached to said frame so that upon contraction of said element a force is applied to said member to move said lever, said element resisting conformance to said member, and a clip having a shape to match said surface, said clip being placed on said member to form said element to the shape of said member so that said element does not spring away from said member to introduce an error in the operation of 5. In a moisture responsive device, a base, a first lever pivotally supported on said base, a moisture responsive element, said element being supported at one extremity by an extremity of said lever, control means, resilient means biasing said control means in a first position means connecting another extremity of said element to said control means, an adjusting screw associated with said base and providing for movement of said first lever with respect to said base, second means connecting said ad- 'justing screw and said control means so that when said adjusting screw is in one extreme position said control means is operated to a second position independent of said element, and means connected to said adjusting screw to relax said element when said adjusting screw is in another extreme position so said control means operates to said first position.

6. A humidistat comprising a mounting bracket, a rotatable adjusting member having a threaded mounting in awall of said bracket and terminating in a free abutment end inwardly of said wall, an electric switch unit having a resilient contact member adapted to move to circuit make and break positions, said contact member requiring an external force to move it to one of said positions and being spring biased to the other of said positions, a push button type plunger adapted to actuate said contact member to one of said positions against its biasing force, a first switch lever of generally bell-crank shape having an arm adapted to depress said plunger button and a lever arm projecting free, an adjusting lever movably supported adjacent the inner abutment end of said adjusting member, a spring biasing said adjusting lever toward the abutment end of said adjusting member, the one end of said adjusting lever projecting free in spaced relation to the free arm of said first switch lever, a humidity element consisting of a length of humidity responsive material connected to the free arm of said first switch lever and the free end of said adjusting lever, a second switch lever fulcrumed at an intermediate point and having its inner extremity adapted to engage and actuate said push button plunger independently of said first switch lever and its outer extremity terminating in the region of said adjusting member, and means rotatable with said adjusting member adapted to engage and actuate said second-named lever for manually controlling the position of said push button plunger independently of the automatic control afforded through responseto changes in relative humidity of said humidity element.

7. A humidistat as claimed in claim 6 wherein said means rotatable with said adjusting member is provided with a radially-projecting cam sector adapted to engage the adjacent end of said second switch lever when the adjusting member is rotated to an extreme position in a direction to stress said humidity element.

8. A humidistat including a humidity element in the form of a length of humidity responsive material, an electric switch unit having a resilient contact member adapted to move to circuit make and break positions; means for actuating said contact member comprising an actuating lever having an arm projecting free and an adjusting lever having a free end spaced from said arm with said humidity element connected between said arm and free end of said adjusting lever; an adjusting member for manually positioning said adjusting lever to adjust the tension of said humidity element, a second lever arranged to actuate said contact member independently of said first-named actuating lever, and means for manually controlling said second lever.

9. A humidistat comprising a mounting bracket, a

rotatable adjusting member having a threaded mounting in a wall of said bracket and terminating in a free abutment end inwardly of said wall, an electric switch unit having a resilient contact member adapted to move to circuit make-and-break positions, said contact member requiring an external force to move it to one of said positions and being spring-biased to the other of said positions, a push button type plunger adapted to actuate said contact member to one of said positions against its biasing force, a first switch lever of generally bell-crank shape having an arm adapted to depress said plunger button and a lever arm projecting free, an adjusting lever movably supported adjacent the inner abutment end of said adjusting member, a spring biasing said adjusting lever toward the abutment end of said adjusting member, said adjusting lever having one end projecting free in spaced relation to said lever arm of said first switch lever, a humidity element consisting of a length of humidityresponsive material connected to said lever arm of said first switch lever and said end of said adjusting lever, a second switch lever fulcrumed at an intermediate point and having its inner extremity adapted to engage and actuate said push button plunger independently of said first switch lever, said second lever having an outer extremity terminating in the region of said adjusting member inwardly of said Wall, a cam secured on the inner extremity of said adjusting member for rotation therewith, said cam having a segment adapted to engage the outer end of said second-named lever when said adjusting member is rotated to one of its'extreme positions and switch lever of generally bell-crank shape having an arm adapted to depress said plunger button and a free projecting lever arm, an adjusting lever pivoted on said base, a spring biasing said adjusting lever toward the abutment end of said adjusting member, said adjusting lever comprising a temperature responsive portion, said adjusting lever projecting free in spaced relation to the free arm of said first switch lever so the movement of said free arm is unaffected by changes in space temperature, a humidity element consisting of a length of material changing in length upon changes in temperature and humidity connected to said free arm and said temperature responsive portion of said adjusting lever whereby said switch is controlled in response to changes in the moisture content of air surrounding said material and is unaffected by changes in temperature.

11. A humidistat comprising a mounting case, a rotatable adjusting member having a threaded mounting in a wall of said case and terminating in a free abutment end inwardly of said wall, an electric switch unit, a push'button type plunger adapted to actuate said switch unit, a first switch lever having one arm adapted to depress said plunger button and a second arm projecting 'free', and adjusting lever pivotally supported on said case and biased against said free abutment end of said adjusting member, said adjusting lever having one end projecting free in spaced relation to said second arm of said first switch lever, a humidity element consisting of a length of humidity-responsive material connected between said one end and said second arm, a second switch lever fulcrumed at an intermediate point and having its inner extremity adapted to actuate said switch unit independently of said first switch lever, said second lever having an extremity terminating in the region of said adjusting member inwardly of said wall, a member secured on the inner extremity of said adjusting member for rota -tiontherewith and adapted to engage the outer end of said second-named lever when said adjusting member is rotated to one extreme position to actuate said switch -unit independently of said first lever, said member having a detent notch, and means for releasably engaging said notch when said member is rotated to said one extreme position for retaining said adjusting member in said one extreme position.

12. A humidistat comprising, a rotatable adjusting member, an electric switch, a push button type plunger adapted to actuate said switch, a first switch lever of generally bell-crank shape having an arm adapted to depress said plunger button and a lever arm projecting free, j i

ran adjusting lever movably supported adjacent an inner abutment end of said adjusting member, a spring biasing said adjusting lever toward said abutment end of said adjusting member, said adjusting lever having one end projecting free in spaced relation to said lever arm of:

said first switch lever, a humidity element consisting of .a length of humidity-responsive material connected to 'said lever arm'of said first switch lever and said end of said adjusting lever, a cam secured on the inner extremity of said adjusting member for rotation therewith, saidcam having a segment adapted to engage the outer end of a second lever when said adjusting member is rotated to one of its extreme positions and to actuate said push button plunger independently of said first lever,

said'cam'having 'a detent notch, and a detent springmeans for releasably engaging said notch when said cam member is rotated to one extreme position for retaining said adjusting member in said one extreme position. a

13. A humidity control including a humidity element in the form of a length of humidity-responsive material, an electric switch unit having a resilient contact member adapted to move to circuit make-and-break positions, said switch having an operating button requiring an external force to operate said switch; and actuating lever having an arm projecting free, a first spring, means connecting said spring to said actuating lever to bias said actuating lever against said operating buttom to provide a predetermined loading force thereon, an adjusting lever having a free end, a second spring, means connecting said second spring to said adjusting lever to bias said adjusting lever, a humidity element changing in length with changes in humidity level, means connecting said humidity element between said arm and said adjusting lever, and adjusting member for manually positioning said adjusting lever for additionally loading said operating button depending on said length of said humidity element.

14. A humidistat including a humidity element in the form of a length of humidity-responsive material, an electric switch unit having a resilient contact member adapted to move to circuit make-and-break positions;

and actuating lever having an arm projecting free, a first spring, means connecting said spring to said actuating lever to bias said actuating lever against said contact member, an adjusting lever having a free end, said adjusting lever comprising a temperature responsive portion which bends with changes in temperature, a second spring, means connecting said second spring to said adjusting lever to bias said adjusting lever in a first direction, a humidity element changing in length with changes in humidity level, means connecting said humidity element between said arm and said adjusting lever, and

tan adjusting member for manually positioning said adjusting lever to adjust the tension on said humidity element, whereby the operation of said switch unit is affected by changes in humidity level and in changes in temperature. V

15. A humidity control comprising a mounting bracket,

-a rotatable adjusting member being mounted in a wall of said bracket, an electric switch unit having a contact member adapted to move to circuit make-and-break positions, said contact member requiring an external force to actuate it to one of said positions and being springbiased to the other of said positions, a member for actuating said contact member against its biasing force, a switch lever of generally bell-crank shape having an arm adapted to depress said member and a lever arm projecting free, an adjusting lever movably supported adjacent said adjusting member, a spring providing a biasing force for biasing the adjusting lever toward a surface of said ad- 'justing member, one end of said adjusting lever projecting free in spaced relation to the free arm of said bell crank lever, a humidity element comprising a length of humidity responsive material connected to the free arm of said bell crank lever and the free end of said adjusting lever, and means associated with said adjusting member to independently actuate said contact member to override the efifect of said humidity element.

16. In a moisture responsive control device, a case,

a switch mounted in said case, a moisture responsive element which changes in length with humidity level ofthe surrounding air, a switch operating means mounted in one end of said case, resilient means for biasing said switch operating means in a first direction, a lever mounted in an opposite end of said case, means connecting said moisture responsive element to said switch operating 9 being adapted to vary the effect of said moisture responsive element on said actuating means to change the level of moisture in the surrounding air needed to close said switch, said cam means having a high portion at one extreme end for engaging said lever to relax said moisture responsive element to obtain a positive actuation of said switch.

17. A humidity control comprising a mounting bracket including a wall, a rotatable adjusting member mounted in said Wall of said bracket, a movable member, means connecting said movable member to said adjusting member, an electric switch unit having a contact member, adapted to move to circuit make-and-break positions, said contact member requiring an external force to actuate it to one of said positions and being spring-biased to the other of said positions, an operating member for actuating said contact member against its biasing force, a switch lever of generally bell-crank shape having an arm adapted to depress said operating member and a lever arm projecting free, an adjusting lever movably supported adjacent said adjusting member, a spring providing a biasing force for biasing the adjusting lever toward a surface of said adjusting member, one end of said adjusting lever projecting free in spaced relation to the free arm of said bell crank lever, a humidity element comprising a length of humidity responsive material connected to the free arm of said bell crank lever and the free end of said adjusting lever, and means including said movable member connecting said adjusting member to independently actuate said contact member to override the effect of a change in length of said humidity element on said contact member.

18. A humidity control comprising a mounting bracket including a wall, a rotable adjusting member mounted in said wall of said bracket, a movable member, means connecting said movable member to said adjusting member, an electric switch unit having a contact member adapted to move to circuit make-and-break positions, said contact member requiring an external force to actuate it to one of said positions and being spring-biased to the other of said positions, an operating member for actuating said contact member against its biasing force, a switch lever of generally bell-crank shape having an arm adapted to depress said operating member and a lever arm projecting free, an adjusting lever movably supported adjacent said adjusting member, a spring providing a biasing force for biasing the adjusting lever toward a surface of said adjusting member, one end of said adjusting lever projecting free in spaced relation to the free arm of said bell crank lever, a humidity element comprising a length of humidity responsive material connected to the free arm of said bell crank lever and the free end of said adjusting lever, and means including said movable member connecting said adjusting member to independently actuate said contact member to a circuit make position to override the eifect of a change in length of said humidity element on said contact member.

References Cited in the file of this patent UNITED STATES PATENTS 2,780,687 Keenan Feb. 5, 1957 2,866,023 Booth Dec. 23, 1958 2,887,544 Gustavsson May 19, 1959 FOREIGN PATENTS 218,145 Germany Jan. 21, 1910 

3. IN A MOISTURE RESPONSIVE DEVICE, A BASE, AN ADJUSTABLE MEMBER ATTACHED AT ONE END OF SAID BASE, A SWITCH MOUNTED ON SAID BASE, SAID SWITCH HAVING A MEMBER FOR ACTUATING SAID SWITCH, A LEVER ATTACHED TO SAID BASE AND ENGAGING SAID MEMBER, SAID LEVER HAVING A FREE END, A FIRST MEMBER PIVOTALLY ATTACHED TO SAID FREE END OF SAID LEVER SAID FIRST MEMBER BEING FREE TO PIVOT ABOUT AN AXIS AND ABOUT A POINT BETWEEN ITS ENDS IN A PLANE OF SAID AXIS, AND A MOISTURE RESPONSIVE RIBBON, SAID RIBBON BEING WRAPPED OVER SAID FIRST MEMBER AND ATTCHED TO SAID MEMBER WHEREBY UPON A CHANGE IN THE LENGTH OF SAID RIBBON AS MOISTURE LEVEL CHANGES SAID LEVER PIVOTS TO ACTUATE SAID SWITCH, SAID FIRST MEMBER PROVIDING FOR THE EQUALIZATION OF TENSION BETWEEN SEPARATE PORTIONS OF SAID RIBBON AND SAID FIRST MEMBER CAN ROCK TO MAINTAIN THE TENSION BETWEEN OPPOSITE SIDES OF SAID RIBBON EQUAL. 